Non-destructive testing of sewer pipes by an acoustical method

Due to defects in sewer systems there is a constant loss of waste water thus polluting the environment. An acoustical impact test device was developed to investigate the condition of sewer pipes. Cracks in the pipe wall can be detected by calculating the arrival times of the waves generated by a hammer impact on the inner pipe surface. Additionally the bedding conditions of sewer pipes can be evaluated by measuring the vibrations excited by the impact resulting in eigenmodes. The natural frequencies of the pipes being investigated were obtained by numerical calculations. The calculations allow precise data analysis yielding good and reproducible results. Numerical and experimental examples are given.